Blasting cartridge



Fb 9, 1943. 1 BARAB 2,3143 BLASTING CARTRIDGE Filed July 16, 1940 FIGTIJACOB BARAB INVENTOR.

BY Nmm...

lented heb. l i943 BLASTNG UTV lw `1 E .lacob Baralt, l

llllercules Powder- Company,

lDel., assigner to Wilmington, lDel.,

a corporation or Delaware Applicationvliuly 16, 1940, Serial No. 345,712

8 Claims.

This invention relates to an improved blasting cartridge and to' methodsof production thereof. It relates more particularly to a blastingcartridge surrounded by a compressible material of low apparent densitywhich provides a cushioning action for the initial explosive shock;

It is the principal object of this invention to provide a' blastingcartridge enclosed in a sheath comprising a compressiblecushioningmaterial. il. iurther object of this invention is to provide asheath comprised of a compressible material and a flame-quenching salt.A further object oi this invention is to provide a low density admiaturewhich may be packed into a tubular sheath for use around an explosivecartridge.

il further object of this invention is to provide an explosive cartridgesurrounded by a low density, tubular sheath which will cushion theinitial shock or the explosion. A still further object oi this inventionis to provide an explosive cartridge which is surrounded by a tubularsheath of low density, compressible material that will give improvedblasting results in operations auch as coal g.

@ther and lurther objects will be apparent hereinafter.

The cushioning oi the initial shock. of a blastlng explosion with acompressible, cushioning material in accordance with this invention isol particular importance toa` explosive cartridges subject to use inproducing high percentages of ,lump material such as is desired in coalmining.

Alter the initial shock of the explosive has been absorbed by thecushioning material, the expanding gases released by the explosion`further expand, but without a shattering force, into the cleavage planesof the seam being blasted with a resulting pushing action which breaksup the structure in such a manner that large firm lumps are obtained.Without the cushioning material about the explosive, the shatteringforce causes a large amount of pulverzed material to be produced. Inparticular, for example, lump coal brings higher prices and anyimprovement which will give a larger percentage of lump in any givenblast constitutes a highly desirable improvement in the blastingoperation necessary in coal mining.

The improvement in blasting cartridges described in accordance with thisinvention may be accomplished with any desired form of explosives, butwill be found most advantageous in connection with, for example, thedynamites developed for use in coal mining. The shattering edect of coalmining explosives, for example, the permissible dynamites, when fired indirect contact with coal, while not of the high order of that obtainedwith straight dynamites, is, nevertheless, undesirable. By sheathingthese explosives, especially the permissbles, a higher percentage oflump coal is obtained.

The improved explosive cartridge which provides the advantage relatedabove in the mining of lum'p coal may be produced in accordance with thepresent invention by surrounding an explosive cartridge with a sheathcomprising an admixture of expanded sodium silicate and a binder; in'addition to the expanded sodium silicate and the binder, the admixturemay, if desirable, include a name-quenching salt. The binders which Ihave found desirable for use with the expanded sodium silicate may bematerials having adhesive properties or material which form materialssuch as, for example, dextrin, clay, waste sulflte liquor, Wood pulp,such as kraft pulp or sulflte pulp, asbestos ber, balsa, bagasse, andother similar binding materials. The name-quenching salt which I havefound to be adaptable for use in my admixture may be, for example,sodium bicarbonate, sodium chloride, borlc acid, ground gypsum, borax,calcium chloride or the like.

The admixture prepared in accordance with this invention may be formedinto a tubular sheath by packing it into an annular ring within asubstantiallyA rigid tube so that the internal diameter thereof isequivalent to the diameter of the explosive cartridge which is to beinserted within the tubular member. The formed sheathing will besemi-rigid and have a cellular, favose structure. The packing of thematerial may be accomplished by machines such as, for example, describedin the co-pending application of R. B. Smith and K. Wassen, Serial No.273,301, filed May 12, 1939.

Having now indicated in a general way the nature and purpose of thisinvention, there follows a more detailed description of preferredembodiments thereof with reference to the accompanying drawing in whichFig. l represents a cushioning sheath partially in section andcontaining an explosive cartridge, and Fig. 2 is a view of thecushioning sheath of Fig. 1l on line i Referring now to the drawing, theassembled article oi this invention comprises a blasting cartridge lsurrounded by a cushioning sheath 2 comprising a packed, homogeneousmaterial 3 retained in position'by a surrounding tube l. 'I'he explosivecartridge I comprises an explosive composition it wrapped by a paperwhich is crimped l at the end.

If desirable, a cap t may be placed over either or both ends of theassembly, but this cap 0 is not generally used. Ihe cap will be founddesirable when a unitary explosive charge is manufactured. The cap maybe placed on the end of the cushioning sheath as shown in Fig. 1 andeither be composed of a sheet of material such as cardboard or the likeor composed of the compressible admixture 3 which surrounds theexplosive cartridge, If it is desirable, the cap may be formed in theshape of a plug and inserted in the end of the sheath 2 proper. In suchinstances the sheath 3 will be slightly longer than the explosivecartridge which is to be used. 'Ihe plugmay be retained by any adhesive,taping or similar expedient.

The thickness of the cushioning material may be varied to providevarying amounts of cushioning edect. A thickness of about V; to aboutinch is desirable for most purposes. Thus, a sheath to fit arounda 11/4by 8 inch. dynamite cartridge will be about 1391 inches, insidediameter, and about 11H- inches 'to about 1H inches outside diameter.This sheath may, of course, be about the same length as the cartridgeand open on both ends in order to aid propagation of the explosive, o rthe ends of the cartridge may be closed with caps or plugs describedhereinbefore, and made either of cardboard or of the sheathingcomposition. 'Ihe closing of the ends of the cartridge slightly retardsthe propagation of detonation from one cartridge to another, but, whenonly one cartridge is to be used in the explosion, the closed end sheathis desirable.

The expanded sodium silicate which is used in accordance with thisinvention is preferably prepared from a commercial sodium silicate ofthe following approximate composition.

` Per cent NazO 19d SOg 62.5 H2O 18.1

This material is a standard article of commerce and consists of smallbeads of hydrated solid sodium silicate. These beads are made by Spraydrying and possess a hollow center surrounded by a relatively thickwall. The material has the property, when heated to about 400 F., ofintumescence; i. e., the material softens suiciently at about 400 F. toallow the steam entrapped in the bead to bulge or blow walls outwardmaking a product of much lower apparent density. For example, theoriginal apparent density of this sodium silicate is in the vicinity of0.75 g./cc., but on expanding drops to as low as 0.025 g./cc. andlsometimes even lower.

If desirable, in making the expanded sodium silicate, it may be treatedto render the expanded material insoluble in water. Surface treatmentsof various kinds may be used. One of the most satisfactory methods tomake expanded sodium silicate for use in the sheaths of this inventionhas been to dehydrate the sodium silicate during the expansionprocedure.

It has been found when there is over about 7% Water in the sodiumsilicate being expanded a material may be produced which is too solubleto be completely satisfactory in the production of sheathing. However,by essentially complete dehydration during the expansion procedure or ofthe expanded material after the procedure so that a material having lessthan about 2% moisture is produced a satisfactory expanded substantiallywater-insoluble silicate is obtained. The pre-dried material may beexpanded so that it loses practically all of its residual water andsamples having less than 2% residua1 moisture have a satisfactoryinsolubility for the production of sheaths.

For example, a pre-dried sample of sodium silicate, containing about 9%H2O when on ex` panding was reduced to 1% residual water was only 5%water-soluble. In a comparable test a material having about 18% moisturewhen on expanding was reduced to only 9% residual water the expandedmaterial was 35% water-soluble.

It was found, however, that when there was only 6-7% moisture in thematerial to be expanded no expansion would take place even if thematerial is given a very high temperature treatment. The water contentof the sodium silicate particles before expansion should be maintainedabove about 8% and the water content of the expanded material kept.below about 2%.

Although the expanded sodium silicate can be produced in densities aslow as 0.025 g./cc., it is desirable to use meterial of somewhat higherapparent density since the walls of the beads have greater mechanicalstrength when the beads are not expanded to their ultimate extent. Thus,a sodium silicate expanded to give an apparent density between about0.10 and about 0.05 g./cc. is the preferred material for use inproducing the cellular, favose sheathing of this invention. Materialshaving a density higher than 0.10 g./cc. may, of course, be used, but itis rather uneconomical to do so since a large amount of expanded sodiumsilicate is required to accomplish the desired lowering in density ofthe sheath.

In processes of formulating sheathing where mechanical strength of theexpanded sodium silicate is not so important, as when a matrix of fiberis used, sodium silicate expanded to its ultimate low density is quitesuitable.

The sheathing in accordance with this invention may comprise as high asabout 50% expanded sodium silicate, but will preferably contain betweenabout 10% and about 25% expanded sodium silicate. The composition anduse of the sheaths are illustrated by the following examples.

Example I Sheaths were made fromtthe following admixture:

' by packing into a spiral-wound paper tube. The

wall thickness of the packed sheaths was 0.233"

and the average Weight of a 11A x 8 sheath, y

Example 2 'Sheathswere made from the following composition:

sodium bicarhnmf g 333.2 Expanded sodium silicate g 71.8 Dextrln bindercc-- 100.0

This composition produced a sheathfor a asiasis its" x 8" explosivecartridge which had a dry weight oi 93 g. with a wall thickness ofapproximately 0.23" and a density of 0.64 g./cc.

in comparison, a sheath having the following composition:

had an average weight' of 119 g. This was delinitely heavierthan thesheath using expanded sodium silicate even though the amount of lowdensity filler and diatomaceous earth used was definitely increased.

in comparing the two sheaths described above, the streh oi the oneincluding expanded sodium silicate was definitely superior to the onecarrying diatomaceous earth. This is shown by results obtained whendried sheaths were crushed in a hydraulic press. The method was to placethe sheaths between two saddles l inch wide and apply hydraulic pressureuntil inch movement tool: place. n this test the crushing strength ofthe sample with expanded silicate was over 150 lbs., while the crushingstrength of the'sample with dlatomaceous earth was only 63 lbs. Thus, itis apparent that the use of expanded sodium silicate shows advantagesover other materials.

Example 3 Sheaths were made on the following composition:

Sodium chloride rg-rl 02.2

f Expanded silicate g 17.0

lDextrin binder -cc 240 Apparent densities around 0.65 were obtained.

Example fi idheaths were made on the iollowing composi- .apparentdensities around 0.05 were obtained.

The above examples, when tested ior strength and compressibliity,compared favorably with sheaths containing sodium bicarbonate andexpanded sodium silicate.

The advantages oi the sheaths of thisV invention'are also apparent inthat only relatively small quantities oi expanded sodium silicate arerequired to obtain the low densities desired. Further, the sheathmaterial has stronger compression coecient and this is highly desirablesince the sheathing is handled and oftentimes is crushed. Sheathing tobe adaptable for use must have sumcient strength to withstand the roughhandling which it obtains in loading and it has been found that thesheathing containing an expanded sodium silicate gives highly desirableresults. Further, it has been found that the strength ofthe ended sodiumsilicate is high enough so that sheathing may be .prepared at anexplosive plant and shipped without insertion of a support within thetube. The sheathings may be shipped in nbrmal cases, and, upon arrivingat the destination, are not broken or crushed. The possibility ofshipping sheaths without supports within the tube'allows a reduction offreight rates and does away with the necessity of removing the supportswhenever the tubes are to be used. Of course, it is possible to ship thesheath around explosive cartridges, but in doing this, the freight ratesare much higher since explosive materials carry premium freight rates.Likewise. it is oftentimes desirable to use explosive cartridges withoutthe sheath around the cartridge, especially when overburden of slatemust be broken out of the way to contact the coal face. By shipping thesheath and explosive cartridges ln separate containers, it is possibleto use one type .explosive within a mine. and this is advantageous sincethe fewer materials there are to be isolated, the more emcient theoperation of the mine becomes.

It will be appreciated that the above details and examples are givenmerely for the purpose of illustrating my invention and are not intendedto limit' the invention. Moreover, many variations in the compositionsand procedures employed may be made .Without departing from the scope ofthe invention.

The present application is a continuation-inpart oi my application filedAugust 17, 1938, Serial No. 225,342, now U. S. Patent No. 2,277,059.

What I claim and desire to protect by Letters Patent is:

l. .dn improved blasting assembly including an explosive cartridgesurrounded by a preformed, annular, tubular sheath comprising betweenabout 10% and about 50% oi expanded sodium silicate and aflame-quenching salt, said sheath characterized by a semi-rigid,cellular, favose structure which is adapted to provide a cushioningaction for the initial explosive shock.

2. An improved blasting assembly including an explosive cartridgesurrounded by a preformed. annular, tubular sheath comprising betweenabout 10% and about 50% of expanded sodium silicate, a binder, aname-quenching salt, said sheath characterized by a semi-rigid,cellular, iavose structure which is adapted to provide a cushioningaction for the initial explosive shock.

3. .im improved blasting assembly including an explosive cartridgesurrounded by a preformed, annular, tubular sheath comprising betweenabout 10% and about 50% of expanded sodium silicate, a matrix, and aname-quenching salt, said sheath characterized by a semi-rigid,cellular, iavose structure which is adapted to provide a cushioningaction for the initial explosive shock.

Il. An improved blasting assembly including an explosive cartridgesurrounded by a preformed, annular, tubular sheath comprising betweenabout 10% and about 50% of expanded sodium silicate and aflame-quenching salt, said sheath characterized by a semi-rigid,cellular favose structure which is adapted to provide a cushioningaction for the initial explosive shock.

5. ein improved blasting assembly including an explosive cartridgesurrounded by a preformed, annular, tubular sheath comprising betweenabout 10% and about 25% of expanded sodium silicate, sodium bicarbonateand a binder, said sheath characterized by a semi-rigid, cellular,favose structure which is adapted to provide a cushioning action for theinitial explosive shock.

6. An improved blasting assembly including an explosive cartridgesurrounded by a preformed,

annular. tubular sheath comprising between about 10% and about 35% ofexpanded sodium silicate, dextrin, and a flame-quenching salt. saidsheath characterized by a semi-rigid, cellular, favose structure whichis adapted to provide a cushioning action for the initial explosiveshock.

7. An improved blasting assembly including an explosive cartridgesurrounded bya preformed annular, tubular sheath comprising beta/eenabout 10% and about 25%. of expanded sodium silicate and wood pulp anda. llame-quenching salt, said sheath characterized by a semi-rigid,

Y xltwd cellular, favose structure which is adapted to provide acushioning action for the initial explosive shoclr.

8. An improved blasting assembly including an explosive cartridgesurrounded by a preformed, annular, tubular sheath comprising betweenabout 10% and about 25% of expanded sodium silicate, sodium bicarbonate.said sheath characterized by a semi-rigid, cellular, favose structurewhich is adapted to provide aicushioning action for the initialexplosive shock.

JACOB BARAB.

